1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: RLC circuit frequency

  1. Nov 20, 2008 #1
    1. The problem statement, all variables and given/known data

    A RLC circuit has a resonance frequency of 6 KHz. When it is driven by a 8 KHz ac generator, it has an impedance of 1 k W. What are R, L and C in the circuit?

    2. Relevant equations

    3. The attempt at a solution

    the equation for the resonant frequency will be
    fo = 1 / 2 π √(L C)
    the equation for the impedence will be
    Z = √[R2 + (XL - XC)^2]
    where XL = 2 π f L

    XC = 1 / 2 π f C
    f = 8 x 10^3 Hz
    fo = 6 x 10^3 Hz
    Z = 1 x 10^3 Ω

    How am I supposed to solve for the three unkowns(R,L,C) with only two equations? Is there a third relationship for R?
  2. jcsd
  3. Nov 20, 2008 #2


    User Avatar
    Homework Helper

    Are you sure there is no impedence at resonance given?
  4. Nov 20, 2008 #3
    No impedance at resonance is given. That's what I was thinking...it'll be impossible to solve if you don't have a relation for R.
  5. Nov 20, 2008 #4


    User Avatar
    Science Advisor
    Gold Member

    Is your circuit series or parallel?
    And what is this: "...it has an impedance of 1 k W"? Do you mean kohm of the circuit or the generator?
  6. Nov 20, 2008 #5


    User Avatar
    Homework Helper

  7. Nov 20, 2008 #6


    User Avatar
    Homework Helper

    I think he used the Latinized W instead of Ω.
  8. Nov 20, 2008 #7
    well, the question was given by my professor. I am 100% sure that there is a peice of informaiton missing from the original question.

    BTW, the RLC is connected in series.
  9. Nov 20, 2008 #8
    It turns out that he forgot to say that the phase angle=45 degrees...ugghhhh....It's an easy one now.

    Thanks for the help!
  10. Nov 20, 2008 #9


    User Avatar
    Homework Helper

    Alrighty then. There's your third equation.

    Good luck.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook